Transmission of small amplitude digital data signals superimposed upon a larger lower frequency carrier signal is known in the art. In applications such as control of electrical gear connected to utility power supply mains, a control device generates control signals that are coupled to the power supply mains for transmission to the electrical gear for controlling the operating conditions of the electrical gear. For lighting applications, light emitting diodes are emerging as a technology that provides energy efficiency, consistent light quality, and control functionality such as dimming, balancing and accurate color mixing.
IEC 62756—Digital Load Side Transmission Lighting Control (DLT) published by the International Electrotechnical Commission, Geneva, Switzerland defines a protocol for simple control of brightness, color, color temperature, and other parameters for the purpose of controlling lighting sources such as Compact self-ballasted Fluorescent Lamps (CFLi), LED light engines, electronic control gear, and any other light source with integrated or external control gear.
FIG. 1 is a block diagram of a lighting system with one control device and at least one control gear of the related art. The power supply mains 5 have a line side or supply side L and a neutral or return line N. The line side L is connected to the control device 10 and the neutral line N is connected to the control device 10 and the control gear 15a . . . 15n. The control device voltage drop VCG is the voltage between the line side L and load side terminal 20 of the control device. The control device current ICD is the current through the load side terminal 20 of the control device. The control gear voltage VCG is the voltage between the pairs of the input terminals 16a . . . 16n, 17a . . . 17n of the control gear 15a . . . 15n. The control gear current ICG is the current through the input terminals 16a . . . 16n of the control gear 15a . . . 15n that is used to modify and maintain the operation of the control gear 15a . . . 15n. The control gear 15a . . . 15n operates in slave mode only and consequently receives information only. The control device 10 operates in master mode only and consequently transmits information only. It should be noted that bi-directional communication is not restricted from the operation of the control device 10 and the control gear 15a . . . 15n. The control data is transmitted from the control device 10 to the control gear 15a . . . 15n as a bi-phase coding or Manchester coding with error detection. The effective transmission rate of the control data is 200 bit/sec at 50 Hz and 240 bit/sec at 60 Hz. The control device 10 and the control gear 15a . . . 15n are compatible with power supply mains 5 voltage that is from approximately 100 V to 347 V. While other structures are possible the specification as written is defined to supply power to two-wire control devices.
FIG. 2 is a block diagram of a control gear 15a . . . 15n of the related art as shown in FIG. 1. The line side L and a neutral N of the power supply mains 5 are connected to a rectifier unit 25 for rectifying the power supply mains 5 voltage. A bypass circuit 30 is connected to the rectifier unit 25 and is designed to carry specified currents as defined for different periods. Connected in parallel with the bypass circuit 30 is a decoupling circuit 35 that decouples the transmitted data from the power supply mains 5 and forwards the transmitted data signal to a processing unit 40. The processing unit 40 acts on the received data information to drive a lamp controller 50. The lamp controller 50 supplies light emitting elements 55 with the necessary currents and voltages for determining the brightness, color, color temperature, such as low pressure discharge lamps □ or LEDs. A decoupling diode 45 is optionally included in the control gear 15a . . . 15n, if the input capacitance of the lamp controller 50 would disturb the reception of the transmission signal.
FIG. 3 is a plot of a half sine wave at the input of the control gear 15a . . . 15n showing the specified periods of the related art. The half sine wave shown has a period that is one half the period of the power supply mains 5 voltage of 50 Hz or 60 Hz. For the function of the control device 10 to the control gear 15a . . . 15n of FIG. 1, the half sine wave is divided into three periods—the supply period, the operating period, and the data period. In the supply period, power is supplied to a control device 10. In the operating period, power is supplied to a control gear 15a . . . 15n. In the data period, the data is transmitted from the control device 10 to the control gear 15a . . . 15n. The supply period lasts from the zero crossing that begins the half sine wave cycle until the power supply mains 5 voltage achieves a voltage level VSW of 60V−0V/+10V for power supply mains 5 voltage that is from 100V to 120V at the time t4. The supply period lasts from the zero crossing time tZC1 that begins the half sine wave cycle until the power supply mains 5 voltage achieves a voltage level VSW of 120V−0V/+15V for power supply mains 5 voltage that is from 200V to 277V at the time t4. The supply period lasts from the zero crossing that begins the half sine wave cycle until the power supply mains 5 voltage achieves the voltage level VSW of 175V−0V/+15V for power supply mains 5 voltage that is approximately 347V at the time t4. This period is approximately 1200 μsec.
The operating period is the time that the power supply mains 5 voltage is greater that the voltage level VSW between the time at the time t4 and the time at the time t6. This period is approximately 7600 μsec. The data period is the time after the operating period that the power supply mains 5 voltage is less than the voltage level VSW and is approximately 1200 μsec from the period t6 to the zero crossing time tZC2 that is the beginning of the next cycle of the half sine wave.
FIG. 4 is a plot of the voltage and current at the input of the control gear during a data time period of the half sine wave of FIG. 3. When the power supply mains 5 voltage is less than the voltage level VSW, the data period begins at the time t6. The current ICG_LC is the current-carrying capability of the control gear 15a . . . 15n during the data period from the time t6 to the zero crossing time tzc2. FIG. 5 is a plot of a Manchester encoded data packet frame prior to modulation of the half sine wave to be applied to the input of the control gear 15a . . . 15n during the data time period. The voltage VCDmin is the voltage level between the line side L and load side terminals 20 of FIG. 1 of the control device 10 when its impedance ZCD is minimal. The voltage VDATA is the signal amplitude of the transmission signal and is the difference of the voltage between the line side L of the power supply mains 5 and load side terminals 20 of the control device 10 between logical states. The amplitude of the data signal is 7.5V+/−0.5V for power supply mains 5 voltage level of 100V and 120V and 15.0V+/−1.0V for power supply mains 5 voltage level of 230V.
FIG. 6 is a plot of a data packet frame modulating the half sine wave of FIG. 3. As described above the data period begins when the power supply mains 5 voltage VMAINS is lower than the voltage level VSW at the time t6. The data packet frame modulated on the power supply mains 5 voltage VMAINS is specified as being present any time between the time t7 and the time t8. The time t7 is specified as being 800 μsec prior to the next zero crossing time tzc2 and the time t8 is specified as being from approximately 250 μsec to time of the next zero crossing tZC. The data packet frame consists of six half-bits that are each 50 μsec+/−7.5 μsec such that the total message length is 300 μsec. The decoupling circuit 35 must be able to detect the presence of the data within time between the time t7 and the time t8 and extract the data packet frame correctly. A data message or telegram is composed of eight data packet frames. FIGS. 7a-7f are plots of the five types of data packet frames illustrating the Manchester coding of the data packet frames of the data of the related art. In FIG. 7a, the data packet frame begins with a start half-bit that is set to a digital “1”. The next four half-bits are the digital “1's” and “0″s” that define two data bits in a Manchester coding. Each data packet frame is terminated with the last half-bit set to the digital “0”. In FIG. 7b, the first data packet frame of a telegram is a “start-of-telegram” frame and the entire frame is to all “1”. The next six data packet frames provide the data and parity that is interpreted as data for controlling the light emitting elements 55 of FIG. 3. The Manchester code is a bi-phase encoding where each data bit has at least one transition during a bit period. In this implementation of the Manchester coding the digital “0” is has a first half bit of a digital “1” and a second half bit of a digital “0”. The digital “1” has a first half-bit of a digital “0” and a second half-bit of a digital “1”. FIG. 7c illustrates a data packet frame of a digital “0, 0”, FIG. 7d illustrates a data packet frame of a digital “0, 1”, FIG. 7e illustrates a data packet frame of a digital “1, 0”, and FIG. 7f illustrates a data packet frame of a digital “1, 1”.
FIG. 8 is a table describing the structure of a telegram formed from multiple data packet frames of the related art. The first data packet frame of a telegram is a “start-of-telegram” frame as shown in FIG. 7b. All subsequent data packet frames of the telegram shall be payload data. Every data packet frame transmission shall start with the most significant bit (MSB) and with each following data packet frame having decreasing significance and shall end with the least significant bit. This structure is valid within every data packet frame and for every part of the telegram with identical type of information. Following the “start-of-telegram” frame, data frames shall be transmitted containing group number in the first data frame. The second data frame contains the first two most significant bits of the telegram type. The first bit of the third data packet frame has the third data bit of the telegram type and a parity bit is the second bit of the third data frame. The remaining data packet frames have the payload data needed to control the control gear 15a, . . . , 15n of FIG. 1 in accordance with the telegram type.
In the first data frame, the control gear 15a, . . . , 15n that do not support group numbers shall react to group number “0” indicating that the commands are broadcast to all control gear 15a, . . . , 15n being controlled by the control device 10. Each control gear 15a, . . . , 15n shall analyze the telegram for framing errors and parity errors, and length error. The parity will determine an error based upon the analysis of the control gear 15a, . . . , 15n and if an error is detected or a telegram is received incompletely or incorrectly, the control gear 15a, . . . , 15n shall ignore the entire telegram and wait for the transmission of the next telegram. The control device 10 transmits the telegrams continuously and may abort a transmission of the telegram and start a new transmission at the next data period of the power supply mains 5.